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Sponge skin

© Narayan Dattatray Wadadekar

Animals fascinate children and even grown up people. One very important reason for the fascination is - animals move and locomote. But do you know there is a group of animals, the phylum Porifera, who never move even a body part leave alone going from place to place?. They are capable of locomotion only as larvae but once they become adults they literally settle down leading a completely sedentary life.

The phylum porifera is the most primitive and ancient group of multicellular animals. Simplest of these animals have a cup shaped body which is completely hollow inside. There are no organs inside. All they have is the skin i.e. the bodywall.

The bodywall of the sponges has two layers of cells. The outer layer is called – pinacoderm or epiderm. Inner layer is known as choanoderm, or gastroderm. These layers are held together by a gluey mesogloea.

A large variety of cells carrying out several different functions are seen in the sponges. As skin is all that the animals have all work to keep the animal alive and even to project itself in to future that is reproduction is done by the skin.

Sponges, have a skeleton of spicules of Calcium, Silica and a protein, Spongin in the form of fibrous network that gives their bodies shape. All these elements may not be there in each variety of a sponge but a given sponge may have one or more of these components. Sponge spicules might be lovely to look at and you may see them at- http://www.ucmp.berkeley.edu/porifera/po...

Here is a list of a variety of skin cells and their functions. Pinacocytes -These cells are flat thin, leathery and tightly packed together to form the pinacoderm.

Choanocytes (collar cells)- These cells are flagellated and are unique to sponges. They line the interior body walls of sponges to form the choanoderm. These cells with their flagella, actively pump out water from the sponge’s interior. They catch food particles. They provide nutrition to the sperm penetrating through them to reach ova. They may develop into gametes. Porocytes – open on pinacoderm and lead water through them into the spongocoel, the cavity in the sponges body. This is a type of cell “ through” which water flows and they have a canal passing through them to reach the spongocoel.

Archaeocytes (ancient cells) - Archaeocytes are totipotent cells they can change into any other type of sponge cells and can even develop into gametes.

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